Gas separation is important in many industries and can typically be accomplished by flowing a mixture of gases over an adsorbent that preferentially adsorbs more readily adsorbed components relative to less readily adsorbed components of the mixture. One of the more important types of gas separation technology is swing adsorption, such as pressure swing adsorption (PSA). PSA processes rely on the fact that under pressure gases tend to be adsorbed within the pore structure of a microporous adsorbent material or within the free volume of a polymeric material. The higher the pressure, the greater the amount of readily adsorbed component will be adsorbed. When the pressure is reduced, the adsorbed component is released, or desorbed. PSA processes can be used to separate gases of a gas mixture because different gases tend to fill the micropore of the adsorbent to different extents.
Another important swing adsorption technique is temperature swing adsorption (TSA). TSA processes also rely on the fact that under pressure gases tend to be adsorbed within the pore structure of a microporous adsorbent material or within the free volume of a polymeric material. One major problem with TSA processes is that as the targeted gas material is adsorbed, the heat in the bed rises due to the exothermic heat released during adsorption. Controlling this rise in temperature is very important to optimizing the overall adsorption efficiency of the bed and the purity of the products produced. When the temperature of the adsorbent is increased, the adsorbed gas is released, or desorbed. By cyclically swinging the temperature of adsorbent beds, TSA processes can be used to separate gases in a mixture when used with an adsorbent that is selective for one or more of the components of a gas mixture.
Various methods of supplying heat to an adsorbent for regeneration cycle of the process have been proposed. These include microwave energy (U.S. Pat. No. 4,312,641), installation of electrical heaters inside the packed adsorbent bed of the adsorber (U.S. Pat. No. 4,269,611), and direct application of an electric current to the adsorber for electrodesorption (U.S. Pat. No. 4,094,652). However, many of the conventional TSA processes have significantly long cycle times, often as long as 12 hours.
TSA has the advantage that by swinging the gas mixture's temperature, instead of the pressure, compression costs can be minimized or even avoided. Another advantage of TSA is that adsorption isotherms are strongly influenced by temperature. Thus, very high purity products can be obtained by adsorbing impurities at low temperature (where adsorption is strong) with the release of a strongly held impurity species being possible by means of high temperature for desorption. However, existing TSA equipment and processes has several disadvantages. For example, the time to swing adsorbent beds over a temperature range sufficient to affect the desired separation can be relatively long, which means that the equipment must be large and as a consequence economically unattractive. Additionally, the construction of properly functioning adsorbent contactors in the art are often of complex design, and are expensive to design and fabricate. Therefore, there is a need in the art for TSA hardware components that can result in shorter cycle times, and are fabricated from readily available materials, thus making the TSA process more economically attractive.